One-step Activation-template Synthesis And Supercapacitor Applications Of Hierarchical Porous Carbon Nanosheets

Supercapacitors have stimulated worldwide interests due to their large power density,high cycle charge and discharge life,wide temperature range,and ultra-high specific capacitance.Supercapacitor electrode materials are an important hub for limiting their large-scale applications.Biomass-based porous carbon material is an environmentally friendly functional material developed in recent decades.It is widely used in supercapacitors because of its low cost,high specific surface area,low density,and environmental protection.The synthesis of porous carbon is usually carried out by an activation method or a template method.The porous carbon synthesized by the template method generally has a low specific surface area,an unreasonable pore structure distribution,high cost,low yield,and the pores are generally mesopores;the porous carbon formed by the activation method generally has a relatively high specific surface area and contains many micropores.However,lack of mesopores restricts its electrochemical performance improvement.Taking into account the above factors,herein,in this dissertation a new one-step activation-template method is proposed to produce a hierarchical porous nanosheet-structured carbon material containing a large number of both micropores and mesopores.Then we have studied in depth the formation mechanism and the electrochemical properties of the hierarchical porous carbon,as well as the verification of its supercapacitor application.The main research contents of this thesis are as follows:1.Porous carbon material was synthesized by a one-step activation-template method by using elm pods powder as the carbon source and potassium permanganate to provide activating agent/template of K₂CO₃ and MnO.The obtained material was characterized to have porous nanosheet-like morphologies with a hierarchical pore size distribution and the average pore size of².7 nm.The largest specific surface area of 2088 m²g^-1 was achieved on the HPCN-6 sample.Notably,the 2.8%nitrogen doping and 8.1%oxygen doping of the HPCN-6 carbon nanosheets could provide pseudocapacitance and enhance the hydrophilic wettability,thus significantly contribute to the total capacitance,laying the foundation for their excellent electrochemical performances.2.The carbon nanosheets were used to fabricate supercapacitor electrodes,and their electrochemical performance was characterized in a three-electrode system.The effects of sample synthesis parameters,such as the precursor ratio and the heating temperature,on the electrochemical performance of the electrode were investigated.The HPCN-6 sample-based electrode was revealed to have a high capacitance of 548.6 F g^-1 at a current density of 1 A g^-1 in the KOH electrolyte with its impedance resistance less than 1?.3.The supercapacitor applications of the hierarchical porous carbon sheets were investigated.Firstly,the electrochemical measurements on the carbon sheets-based electrode using KOH electrolyte were performed.The capacitance of the electrode reached to 324 F g^-1 at 1 A g^-1 and remained above 98%after 10 000charge and discharge cycles.Secondly,1-ethyl 3-methylimidazolium tetrafluoroborate ionic liquid electrolyte was used to explore electrochemical properties of the electrode.A high capacitance of 230 F g^-1 at high voltage range of 4 V was achieved.The obtained maximum energy density of the electrode was as high as 125.5 Wh kg^-1 at a power density of 991 W kg^-1,which is one of the highest energy density obtained for biomass-based carbon materials.Finally,a supercapacitor device based on porous carbon nanosheets was assembled successfully realized the operation of an electrical fan.